The present invention relates generally to scanning imaging devices and, more specifically, to a high spatial resolution rotation catheter for use in optical coherence tomography or the like.
When light reflected from samples interferes with a reference beam, the frequencies of the interfering signals reveal the depth where the light is reflected. This technique has been used in imaging, known as Optical Coherence Tomography (OCT). OCT is an optical signal acquisition and processing method allowing extremely high-quality, micrometer-resolution, three-dimensional images from within optical scattering media (e.g., biological tissue) to be obtained. Scanning imaging probes are used in OCT and other interferometric imaging and ranging systems, as well as for delivery of other imaging modalities or therapeutic optical sources. See, e.g., U.S. Pat. No. 6,891,984, which is incorporated herein by reference in its entirety.
Typical fiber rotation probes for OCT imaging include fiber GRIN (Gradient-Index) lenses and micro-prisms. The disadvantage of using a micro-prism is that the emitting surface is curved. This curved surface acts as a cylinder lens that degrades the laser beam quality. The focal spot is in an elliptical shape rather than a circular shape. Polishing the curved surface of the fiber into a flat surface would solve this problem, but the mechanical processing could be very difficult. The high cost of the mechanical processing is another issue, since the fiber size micro-prisms (e.g., about 0.125 mm in diameter) that are attached to the fiber GRIN lenses are not suitable for mass production. The polished micro-prisms also require a clear tubing to form a kind of air bag to protect the polished surface in order to achieve a full internal reflection. Another disadvantage is the need for a fluid occupying the space between the prism and the inner sheath of the catheter in order to balance optical aberrations due to cylindrical lens effect. See, e.g., U.S. Patent Application Publication No. 2011/0137124. As such, the distal end of the stationary part of the catheter must be open, making it vulnerable to dust contamination.
Alternatively, fiber rotation probes for OCT imaging using fiber GRIN lenses and micro-mirrors are also a popular design. One benefit of using a micro-mirror instead of a micro-prism is that there is no cylinder lens effect. The high cost of processing remains an issue, however, since the small size micro-mirrors are not commercially available and the processing cost for polishing and coating each micro-mirror to provide a highly reflective surface is very high. Currently, micro-mirrors are about 0.5 mm in diameter. Heretofore, micro-mirrors having a diameter of at most about 0.25 mm have not been made successfully.